Skip to content

Teeth of Small, Feathered Dinosaurs Tell a Story of Extinction and Survival

April 21, 2016

Today, my research group published a new paper in the journal Current Biology addressing one of the biggest mysteries of the end Cretaceous mass extinction event- why the did the ancestors of living birds survive, but contemporary small, feathered raptor dinosaurs and primitive toothed birds go extinct?

Our research provocatively suggests that at least some groups of living birds may have their ancestors’ beaks to thank for surviving the asteroid impact and resulting mass extinction that wiped out the dinosaurs.  We show the closest relatives of modern birds, the small feathered raptor dinosaurs and primitive toothed birds, went extinct abruptly at the end of the Cretaceous Period, and that beaked birds may have benefited because of their ability to eat seeds. The study was led by University of Toronto PhD student Derek Larson (now at the Philip J. Currie Museum) and included Dr. Caleb Brown, who graduated a couple of years ago and is now at the Royal Tyrrell Museum– the study took almost five years to complete.

larson_2016_image_1

Small, feathered theropod diversity of the Hell Creek Formation, immediately before the asteroid impact. Credit: Danielle Dufault

Several recent studies have suggested that large herbivorous dinosaurs were decreasing in diversity in the last few million years leading up to the end Cretaceous extinction event.  We were interested in seeing if small, feathered dinosaurs and early birds followed this pattern. But their fossil record is extremely fragmentary in the last 20 million years of the Age of Dinosaurs. Therefore, it is difficult to quantify just how many species there were  at any given time and how that changed. The only consistent and informative fossil indicator of their diversity is their teeth- which are abundantly preserved in microfossil bone beds. Interestingly, tooth shape is a key indicator of diet, so we reframed the question from how diverse they were in terms of species, to one that traced the breadth of feeding niches they occupied in the time leading up the extinction event. This would actually provide us with even more information because we could look at the ecology of their extinction.

So we analyzed more than 3,000 of these teeth to give the highest resolution picture of their changing shape and diets over the last 20 million years of the Age of Dinosaurs. The teeth of these bird-like dinosaurs and primitive toothed birds to show that these dinosaurs were a consistent and stable part of the ecosystem leading up to the end of the Cretaceous. There was no evidence of a long term decline- they went extinct very suddenly in geological terms.

Preserved bird and bird-like dinosaur teeth examined in this study were likely suited to eat a variety of animals- insects and small vertebrates.  However, modern birds (Neornithes) are characterized by the shared presence of a toothless beak-so we hypothesized that diet might have been a key factor in their survival. And if the feathered bird-like dinosaurs that ate animals went extinct, perhaps birds survived because they could eat plants, or more specifically, seeds. In the conditions in the wake of the asteroid impact, global forest fires raged and the sun was blocked out by debris ejected into the atmosphere. The ecosystem would quickly lose foliage and animal life. The tooth maniraptoran and early birds were tied to photosynthetic food webs, and my have been more likely to perish.  But seeds would be high-energy packets of food that would persist on the landscape, and any animal that could access them would have an ecological advantage. IF the ancestors of at least some groups of modern birds could access this resource in the critical time period immediately after the impact, that could have been vital.1-fossilteethsThe bird fossil record at the end of the Cretaceous is very incomplete, so the ecologies of species that survived the mass extinction are still largely unknown. With little direct evidence of fossil species surviving the extinction, the reasons as to why some species were able to survive the extinction while their closest relatives went extinct have been unclear.  So we looked to living birds to see if we could test our idea. First, we used the latest family tree of living birds to see if seed-eating was the primitive diet of the early ancestors of living birds.  The data clearly infer that the earliest branches of the bird family tree were likely seed eaters that preferred terrestrial habitats, and were unlikely to be waterbirds- as has been previously suggested. So these groups would have been around when the asteroid hit, and could have benefited from eating seeds during this global crisis. We then looked to present day ecological studies to see what bird flourish in disturbed habitats. Interestingly, it turns out that seed-eating birds are very typically the first vertebrates back into disturbed habitats ravaged by forest fires. This makes sense, because a forest fire will burn all the foliage and decimate the animal population, but seeds can survive in their protective shell, and they can lie dormant for decades, providing food for seed-eating birds.

Its important to keep in mind that extinction patterns at the end of the Cretaceous are complex and involved multiple factors, and we are not proposing that the only reason crown birds survived was seeds. Body size, sensory and metabolic differences, and other factors may have also contributed, and conditions would have affected different bird lineages differently. But small teeth have given us big insights into the extinction patterns of bird-like dinosaurs and primitive birds, and a better understanding of how diet might have played a role in the survival of crown-group bird groups in the wake of the asteroid impact.

Read the paper:

Larson, D.W., C. M. Brown, and D. C. Evans. Dental Disparity and Ecological Stability in Bird-like Dinosaurs prior to the End-Cretaceous Mass Extinction. Current Biology: DOI: http://dx.doi.org/10.1016/j.cub.2016.03.039

Additional Coverage:

Toronto Star story here.

Globe and Mail Story here.

CSM story here.

CBC story here.

Derek on Quirks & Quarks here.

Introducing Wendiceratops

July 8, 2015
Life reconstruction of Wendiceratops pinhornesis by Danielle Dufault

Life reconstruction of Wendiceratops pinhornesis by Danielle Dufault

Today, Michael Ryan and I published a paper describing a new species of horned dinosaur, Wendiceratops pinhornesis. It is one of the oldest known members of Ceratopsidae, the family of large-bodied horned dinosaurs that includes Triceratops, and it provides new information on the early evolution of skull ornamentation in this iconic group of dinosaurs characterized by their horned faces.

7_Wendiceratops_quarry_by_DavidEvans

The quarry in southern Alberta where Wendiceratops was excavated.

The bonebed that produced all of the known Wendiceratops fossils is located in southern Alberta, and in rocks of the lowest part of the Oldman Formation that date to approximately 79 million years. The site was discovered in 2010 by Wendy Sloboda, when she was prospecting for new fossil sites as part of our field team. She found numerous bones, including parts of the distinctive frill, coming out of a mud rock layer at the bottom of a very steep hill. In order to uncover more bones, out team had to remove over 20 meters (60 ft) rock above the bonebed layer, which took an entire field season. We started excavation of the site in the summer of 2011, and have collected over 220 bones to date, representing  multiple individuals preserved at different growth stages. The recovered bones represent the majority of the skeleton. This makes Wendiceratops one of the best-known early members of the Ceratopsidae.

Skeletal reconstruction of Wendiceratops pinhornensis by Danielle Dufault.

Skeletal reconstruction of Wendiceratops pinhornensis by Danielle Dufault.

Wendiceratops was about 7 m (20 ft) long, and weighed between 1 and 2 tons when alive- about the size of a hippo. Wendiceratops is distinguished from other horned dinosaurs by an impressive array of gnarly horns curling forward off the back of its neck shield. It also had a prominent, upright horn over the nose, and may have had large brow horns as well, although we have not found this part of the skull.

Wendiceratops means “Wendy’s horned Face”, and it is named after Wendy Sloboda, who discovered the first skull bones of the dinosaur in the remote badlands along the Milk River.  Wendy is legendary for her ability to find fossils in Alberta , where she has discovered literally hundreds of important specimens; more than 2000 specimens are attributed to her in the Royal Tyrell Museum of Palaeontology collections. Given her outstanding contributions to our understanding dinosaurs in Alberta, she deserves a dinosaur.

Mounted skeleton of Wendiceratops on display at the Royal Ontario Museum, Toronto.

Mounted skeleton of Wendiceratops on display at the Royal Ontario Museum, Toronto.

Collecting the bones, preparing them, and mounting them for exhibit was a huge effort, and this was documented in the documentary series Dino Hunt Canada, which celebrates the incredible dinosaur fossil record of the country (find out more at http://dinohuntcanada.history.ca/). The Wendiceratops project could not have been done without the help of dozens of university students and volunteers helping out with the dig, hundreds of hours of work by skilled technicians in the lab, and our exhibits team- I can’t thank them enough.  A full size skeleton of Wendiceratops and an exhibit documenting its discovery is currently on display at the Royal Ontario Museum in Toronto.

 

Learn more about Wendiceratops here.

Read the Open Access scientific paper:

David C. Evans and Michael J. Ryan, “Cranial Anatomy of Wendiceratops pinhornensis gen. et sp. nov., A Centrosaurine Ceratopsid from the Oldman Formation (Campanian), Alberta, Canada, and the Evolution of Ceratopsid Nasal Ornamentation.” PLoS One. DOI: 10.1371/journal.pone.0130007

Congrats to Dr. Kirstin Brink!

June 13, 2015

KB_CTKirstin Brink successfully defended her Ph.D. in the Department of Ecology and Evolutionary Biology at the University of Toronto this past Monday. Here thesis is entitled “Phylogenetics and Dental Evolution in Sphenacodontidae (Synapsida)”. Her thesis explores the importance of dental histology for identifying tooth characters for phylogenetic analyses, as well as understanding feeding ecology changes through time in the oldest terrestrial apex predator,  the iconic sail-backed Dimetrodon. ABSTRACT: Paleozoic sphenacodontid synapsids are the oldest known fully terrestrial apex predators, distinguished by strong heterodonty, massive skulls, and well-developed labio-lingually compressed, recurved teeth with mesial and distal cutting edges (carinae). Dimetrodon is an Early Permian (295–272 Ma) sphenacodontid known from southern USA, Canada, and Germany. Dimetrodon is of exceptional importance as it is the most abundant and speciose sphenacodontid, providing valuable information on issues related to the origin of therapsids. Thirteen species of Dimetrodon are currently recognized from hundreds of specimens, but many of these taxa are primarily identified on the basis of size, stratigraphic, and geographic locations. Therefore, little is known about the relationships among species of Dimetrodon or the role they and other sphenacodontids played as apex predators in shaping Early Permian ecosystems. A robust, species-level phylogeny of sphenacodontids will allow for the examination of evolutionary patterns within the clade. The first in-depth description, including histological analyses of several species of Dimetrodon, reveals that the dentition is diverse and bears species-specific morphology. Tooth morphology includes simple carinae with smooth cutting edges and elaborate enamel features, including the first occurrence of cusps and true denticles (ziphodonty) in the fossil record, and the first description of plicidentine in synapsids. The first species-level time calibrated phylogenetic analysis for sphenacodontids, including the enigmatic Bathygnathus borealis, indicates that significant changes within the clade are related to the dental apparatus. This suggests that the morphological changes in sphenacodontids are associated with changes in feeding style and trophic interactions in these ecosystems. The results presented in this thesis are the first steps towards a more comprehensive understanding of evolutionary changes within sphenacodontids and highlights innovations in the group, including the first adaptations towards hypercarnivory.

Congrats to Kirstin on completing her degree. I also want to thank her for her help setting up and running the palaeohistology lab at the ROM.  Kirstin is moving on to a prestigious Killam Postdoctoral Fellowship at the University of British Columbia, working with Dr. Joy Richmond, starting in September.

Evolution of Dinosaur Skin and Feathers: A Complex Story

June 2, 2015

Today, Paul Barrett from the Natural History Museum, Nicolas Campione, a lab alumnus and researcher at Uppsala University, and I published a detailed study of the evolution of dinosaurian integument. Despite extensive recent speculation, our analyses suggest that the majority of non-avian dinosaurs were more likely to have scales than to exhibit ‘feather-like’ structures that are the direct precursors to the feathers we see in modern birds.

Over the past two decades, a number of spectacularly preserved dinosaur fossils with feathers have revolutionized the field of palaeontology. The presence of feathers in birds and their immediate dinosaurian ancestors – theropods like Velociraptor – is uncontroversial, but the presence of true feather homologues, or protofeathers, in other major groups, such as ornithischian dinosaurs, has been highly debated. Several recent discoveries have suggested that, along with scales, filament-like ‘protofeathers’ might have been present in the common ancestor of all dinosaurs and ubiquitous in the entire group.

In order to test the idea that dinosaurs were primitively feathered,  we compiled a comprehensive database of dinosaur skin fossils- the most complete to date- and attempted to reconstruct the evolutionary history of dinosaur scales and feathers using a maximum likelihood approach. Most of our analyses provide no support for the appearance of feathers in the majority of non-avian dinosaurs, and although many meat-eating dinosaurs were feathered, the ancestor of all dinosaurs was probably scaly. Interestingly, the quills and filaments in some major plant-eating ornithischian dinosaur groups were evolutionary experiments that were independent of true feather origins.

Fossilized impression of the scaly skin of the sauropod dinosaur Barosaurus lentus.

Fossilized impression of the scaly skin of the sauropod dinosaur Barosaurus lentus.

Untangling when particular integumentary features first evolved will help us understand the origins of feathers and why they first arose, but our analyses are limited to the data we have at hand and questions still remain. Importantly, our research also quantifies taphonomic biases and identifies gaps in the fossil record of dinosaur skin. The biggest and most significant gap is in the Triassic and Early Jurassic, when dinosaurs first originated and diversified, where very few integument fossils are known. Rocks of this age also lack significant lake/lagoonal fossil sites where delicate feather-like structures are preferentially preserved. This makes the origin of the direct filamentous precursors to feathers difficult to pinpoint. Whether or not the first dinosaurs had true ‘protofeathers’ may only be finally resolved with the discovery of more fossils, particularly from early in dinosaur evolutionary history.

Reference:

P. M. Barrett, D. C. Evans, and N. E. Campione. 2015.  Evolution of dinosaur epidermal structures. Biology Letters. 20150229. Doi: http://dx.doi.org/10.1098/rsbl.2015.0229

Press Release:

Origins of feathered dinosaurs more complex than first thought

Media:

Feathers or scales? New research highlights dinosaur diversity

Most dinosaurs had scales, not feathers, fossil analysis concludes

Dino Hunt Canada Series Airs on HISTORY Canda

February 28, 2015

DinoHunt CanadaIn the last century, nearly 1,000 dinosaur skeletons have been found in Canada, with more being discovered every year. Canada is one of the best places in the world to trace the evolutionary story of dinosaurs – from their first steps to the peak of their diversity and to their ultimate extinction. Through an exciting multi-platform experience, HISTORY travels coast-to-coast with Canada’s top palaeontologists to uncover how dinosaurs lived – and died – right here at home. Dino Hunt Canada is a new 4-part documentary series that tells the story of six teams of Canadian fossil hunters who discover some of the most important dinosaur finds in the world.  Their expeditions take viewers to some of the most stunning locations in Canada, from the red sandstones of Nova Scotia’s Bay of Fundy to the moonscape of the Canadian Badlands in Alberta.

The Dino Hunt Canada digital experience (www.dinohunt.ca) provides Canadians with a fun and engaging, cross-platform glimpse into the discovery of a new dinosaur. You can follow its complete journey beginning with the discovery of the fossils in Alberta, through scientific study and restoration via a live-streaming online feed running directly from the ROM’s Dino Lab, all the way to its eventual reconstruction and public display. The website also offers users the opportunity to Ask an Expert – one-on-one access to the palaeontologists and experts from the miniseries, and learn more about Canada’s rich dinosaur history through the Dino Index’s 3D dino models with added images and encyclopedic text. Through the online “Name Our Dino”contest, Canadians nicknamed the new skeleton “Cornelius”.

DinoHuntWeb

To learn more about Canada’s amazing dinosaur heritage, visit http://www.DinoHunt.ca.

The first episode, features my team from the Royal Ontario Museum (ROM) as we search for the skull bones of what turns out to be a previously unknown horned dinosaur. The newly discovered dinosaur is on display in the New Dino Discovered exhibition, which opened  to the public during the ROM’s Dinos Invade! Big Weekend on January 24 and 25. The exhibition features a cast of the new species, as well as information that takes visitors into the field with us as we dig up the fossils.

Canada's newest dinosaur, a yet-to-be named ceratopsian, on display in the New Dino Discovered exhibit at the Royal Ontario Museum

Canada’s newest dinosaur, a yet-to-be named ceratopsian, on display in the New Dino Discovered exhibit at the Royal Ontario Museum

Hear an interview about the new dinosaur discovery here.

To learn more about Canada’s amazing dinosaur heritage, visit www.DinoHunt.ca.

Introducing Mercuriceratops

June 18, 2014

New Horned Dinosaur Reveals Unique Wing-Shaped Headgear

Today, we annnouce the discovery of  a new species of horned dinosaur (ceratopsian) based on fossils collected from Montana in the United States and Alberta, Canada. Mercuriceratops (mer-cure-E-sare-ah-tops) gemini was approximately 6 meters (20 feet) long and weighed more than 2 tons. It lived about 77 million years ago during the Late Cretaceous Period. Research describing the new species is published online in the journal Naturwissenschaften.

Mercuriceratops (middle) compared to a typical centrosaurine (left) and chamosaurine (right). Courtesy Danielle Dufault.jpg

Mercuriceratops (middle) compared to a typical centrosaurine (left) and chasmosaurine (right). Courtesy Danielle Dufault.

Mercuriceratops (Mercuri + ceratops) means “Mercury horned-face,” referring to the wing-like ornamentation on its head that resembles the wings on the helmet of the Roman god, Mercury. The name “gemini” refers to the almost identical twin specimens found in north central Montana and the UNESCO World Heritage Site, Dinosaur Provincial Park, in Alberta, Canada. Mercuriceratops had a parrot-like beak and probably had two long brow horns above its eyes. It was a plant-eating dinosaur.

Mercuriceratops took a unique evolutionary path that shaped the large frill on the back of its skull into protruding wings like the decorative fins on classic 1950s cars. It definitively would have stood out from the herd during the Late Cretaceous,” said lead author Dr. Michael Ryan, curator of vertebrate paleontology at The Cleveland Museum of Natural History. “Horned dinosaurs in North America used their elaborate skull ornamentation to identify each other and to attract mates—not just for protection from predators. The wing-like protrusions on the sides of its frill may have offered male Mercuriceratops a competitive advantage in attracting mates.”

“The butterfly-shaped frill, or neck shield, of Mercuriceratops is unlike anything we have seen before,” said co-author Dr. David Evans, curator of vertebrate palaeontology at the Royal Ontario Museum. “Mercuriceratops shows that evolution gave rise to much greater variation in horned dinosaur headgear than we had previously suspected.”

The new dinosaur is described from skull fragments from two individuals collected from the Judith River Formation of Montana and the Dinosaur Park Formation of Alberta. The Montana specimen was originally collected on private land and acquired by the Royal Ontario Museum. The Alberta specimen was collected by Susan Owen-Kagen, a preparator in Dr. Philip Currie’s lab at the University of Alberta. “Susan showed me her specimen during one of my trips to Alberta,” said Ryan. “When I saw it my jaw dropped open as I instantly recognized it as being from the same type of dinosaur that the Royal Ontario Museum had from Montana.”

The holotype squamosal of Mercuriceratops from Montana (left) and the referred specimen from Alberta (right)

The holotype squamosal of Mercuriceratops from Montana (left) and the referred specimen from Alberta (right)

The Alberta specimen confirmed that the fossil from Montana was not a pathological specimen, nor had it somehow been distorted during the process of fossilization,” said Dr. Philip Currie, professor and Canada research chair in dinosaur paleobiology at the University of Alberta. “The two fossils—squamosal bones from the side of the frill—have all the features you would expect, just presented in a unique shape.”

This dinosaur is just the latest in a series of new finds being made by Ryan and Evans as part of their Southern Alberta Dinosaur Project, which is designed to fill in gaps in our knowledge of Late Cretaceous dinosaurs and study their evolution. This project focuses on the paleontology of some of oldest dinosaur-bearing rocks in Alberta and the neighbouring rocks of northern Montana that are of the same age.

Body Mass Evolution and Adpative Radiation in Dinosaurs

May 6, 2014

Today we announced the results of a major study on dinosaur body size evolution in a new paper published in PLoS Biology.

From the Press Release: An international, led by scientists at Oxford University and the Royal Ontario Museum, estimated the body mass of 426 dinosaur species based on the thickness of their leg bones. The team found that dinosaurs showed rapid rates of body size evolution shortly after their origins, around 230 million years ago. However, these soon slowed: only the evolutionary line leading to birds continued to change size at this rate, and continued to do so for 170 million years, producing new ecological diversity not seen in other dinosaurs.

Dinosaurs evolved into a huge range of shapes and sizes over 170 million years. Courtesy of Julius Csotonyi.

Dinosaurs evolved into a huge range of shapes and sizes over 170 million years. Courtesy of Julius Csotonyi.

“Dinosaurs aren’t extinct; there are about 10,000 species alive today in the form of birds. We wanted to understand the evolutionary links between this exceptional living group and their Mesozoic relatives, including well-known extinct species like T. rex, Triceratops, and Stegosaurus,” said Dr Roger Benson of Oxford University’s Department of Earth Sciences, who led the study. “We found exceptional body mass variation in the dinosaur line leading to birds, especially in the feathered dinosaurs called maniraptorans. These include Jurassic Park’s Velociraptor, birds, and a huge range of other forms, weighing anything from 15 grams to 3 tonnes, and eating meat, plants, and more omnivorous diets.”

The team believes that small body size might have been key to maintaining evolutionary potential in birds, which broke the lower body size limit of around 1 kilogram seen in other dinosaurs.

“How do you weigh a dinosaur? You can do it by measuring the thickness of its leg bones, like the femur. This is quite reliable,” said Dr Nicolás Campione, of the Uppsala University, a member of the team. “This shows that the biggest dinosaur Argentinosaurus, at 90 tonnes, was 6 million times the weight of the smallest Mesozoic dinosaur, a sparrow-sized bird called Qiliania, weighing 15 grams. Clearly, the dinosaur body plan was extremely versatile.”

The team examined rates of body size evolution on the entire family tree of dinosaurs, sampled throughout their first 170 million years on Earth. If close relatives are fairly similar in size, then evolution was probably quite slow. But if they are very different in size, then evolution must have been fast.

“What we found was striking. Dinosaur body size evolved very rapidly in early forms, likely associated with the invasion of new ecological niches. In general, rates slowed down as these lineages continued to diversify,” said Dr David Evans at the Royal Ontario Museum, who co-devised the project. “But it’s the sustained high rates of evolution in the feathered maniraptoran dinosaur lineage that led to birds – the second great evolutionary radiation of dinosaurs.”

The evolutionary line leading to birds kept experimenting with different, often radically smaller, body sizes – enabling new body ‘designs’ and adaptations to arise more rapidly than among larger dinosaurs. Other dinosaur groups failed to do this, got locked in to narrow ecological niches, and ultimately went extinct. This suggest that important living groups such as birds might result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years, which could not be observed without fossils.

Open-Access Article:

Benson R. B. J., N. E. Campione, M. T. Carrano, P. D. Mannion, C. Sullivan, P. Upchurch, and D. C. Evans. 2014. Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage, PLOS Biology 12(5): e1001853.

PLoS Biology Primer:

Moen D, Morlon H (2014) From Dinosaurs to Modern Bird Diversity: Extending the Time Scale of Adaptive Radiation. PLoS Biology 12(5): e1001854

ScienceNOW: How Birds Survived the Dinosaur Apocalypse by Michael Balther